Portion of a tractor



FIG. 1 is a front perspective view of a portion of a tractor showing my new design;

FIG. 2 is a left side view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is an elevated front perspective view thereof.

The broken lines in FIGS. 1 through 6 illustrate portions of the tractor that are not part of the claimed design. 

The ornamental design for a portion of a tractor, as shown and described. 